A new watch-like gadget can measure UV exposure and tells users when they are about to get burnt, without them missing out on all-important vitamin D. The gadget was created to negate the need for suncream, which protects skin from harmful effects of the sun’s rays but also stops the skin from absorbing UVB rays used to make vitamin D. Experts fear such creams have caused a worldwide deficiency.

It is hoped that the watch will help people overcome the problems of vitamin D deficiency. Using the gadget begins by inputting an estimated skin sensitivity, on a scale of 1 to 11. ‘There are huge numbers of people who are aware the sun is healthy, but don’t know how much they need.

‘UVB gives you vitamin D and UVA tends to give you more sun damage.’ Vitamin D is important for managing the body’s calcium levels and maintaining healthy bones, and has also recently been thought to have an effect on breast cancer, arthritis and diabetes.

Barbara Boucher who researches vitamin D at Queen Mary University of London, said: ‘This is an interesting gizmo and provided that the calibration is reasonably accurate, for both the UVB and for the sensitivity to sunlight, it could be a useful safeguard against sunburn.’

However, she was frank about its possible shortcomings, saying: ‘Worn on the wrist, it only tells you about sunlight on that wrist and not how much vitamin D one might make during exposure, since the rest of the arms could be covered up.’

The latest version is on sale for $50, but is expected to be upgraded with a new version which will have Bluetooth capability linking to a smart phone app. The team that produced the original is also working on a sensor that will be able to differentiate between UVA and UVB rays.

Other UV tracking bands are due to be released later this year, such as Netatmo June, a UV sensor disguised as jewellery.